Liquid injector for injecting contrast medium at variable rate into a subject who is to be imaged by imaging diagnostic apparatus

ABSTRACT

A liquid injector registers the data of a variable pattern in which an injection rate of a contrast medium varies with time. The injection rate of the contrast medium varies with time according to the variable pattern for maintaining a state in which the image contrast achieved by the contrast medium approximates an optimum level.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/657,440, filed Sep. 8, 2003, which claims priority to Japanese PatentApplication No. 2002-281109, filed Sep. 26, 2002, the content of whichis incorporated herein it its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid injector for injecting aliquid into a subject, and more particularly to a liquid injector forinjecting a liquid into a subject who is to be imaged by an imagingdiagnostic apparatus such as a CT (Computed Tomography) apparatus, anMRI (Magnetic Resonance Imaging) apparatus, an angiography apparatus, orthe like.

2. Description of the Related Art

Presently available imaging diagnostic apparatus for capturingfluoroscopic images of subjects include CT scanners, MRI apparatus, PET(Positron Emission Tomography) apparatus, ultrasonic diagnosticapparatus, CT angiography apparatus, MR angiography apparatus, andultrasonograph.

When such an imaging diagnostic apparatus is used to capture afluoroscopic image of a subject, it is occasionally practiced to injecta liquid such as a contrast medium or a saline solution into thesubject. There have been liquid injectors in practical use forautomatically injecting a liquid into a subject (see, for example,patent documents 1, 2 below).

Patent document 1: Japanese laid-open patent publication No. 2002-11096;

Patent document 2: Japanese laid-open patent publication No.2002-102343.

Such a liquid injector has a liquid injection mechanism comprising adrive motor and a slider mechanism, and employs a liquid syringe that isremovably mounted on the liquid injection mechanism. The liquid syringecomprises a cylinder and a piston slidably inserted in the cylinder. Thecylinder is filled with a liquid, e.g., a contrast medium, to beinjected into the subject.

The liquid syringe is connected to the subject by an extension tube andset on the liquid injection mechanism. The liquid injection mechanismindividually holds the piston and the cylinder and moves them relativelyto each other for injecting a liquid, typically a contrast medium, fromthe liquid syringe into the subject. If the operator of the liquidinjector enters the data of an injection rate for the contrast mediuminto the liquid injector, then the liquid injector injects the contrastmedium into the subject at the injector rate whose data have beenentered into the liquid injector. The injected contrast medium changesthe image contrast of the subject, allowing the imaging diagnosticapparatus to capture a good fluoroscopic image of the subject.

Thus, the liquid injector can inject a contrast medium into a subject tobe imaged by an imaging diagnostic apparatus in order to change theimage contrast of the subject so that the imaging diagnostic apparatusis able to capture a good fluoroscopic image of the subject.

There has been conducted an experiment in which a contrast medium for CTwas actually injected into a subject by a liquid injector and a CT valuerepresenting an image contrast was measured. The results of theexperiment have indicated that, as shown in FIG. 11 of the accompanyingdrawings, the CT value increased nonlinearly and then quickly decreased,and remained at an optimum level only for a short period of time.Therefore, even when a contrast medium is injected into a subject usingthe conventional liquid injector, it is difficult for the imagingdiagnostic apparatus to capture a good fluoroscopic image of thesubject.

Moreover, as shown in FIG. 11, the CT value has its peak level muchhigher than the optimum level, indicating that the subject is dosed withan excessive amount of contrast medium. Consequently, the contrastmedium is consumed too much, and tends to adversely affect the subject'shealth. Simply reducing the amount of contract medium to be injectedinto the subject would not solve the problem because the period of timein which the CT value approximates the optimum level would be reduced,making it more difficult to capture a good fluoroscopic image of thesubject.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a liquidinjector which is capable of injecting a contrast medium into a subjectin order to maintain a state in which the image contrast produced by theinjected contrast medium approximates an optimum level.

A liquid injector according to the present invention has a liquidinjection mechanism, a pattern storing means, and a rate controllingmeans. The liquid injection mechanism injects a contrast medium into asubject whose fluoroscopic image is to be captured by an imagingdiagnostic apparatus. The pattern storing means registers data of avariable pattern in which an injection rate of the contrast mediumvaries with time. The rate controlling means varies an operating speedof said liquid injection mechanism with time according to said variablepattern. Since the injection rate of the contrast medium varies withtime according to the variable pattern, a state in which the imagecontrast achieved by the contrast medium approximates an optimum levelis maintained. Therefore, an optimum fluoroscopic image of the subjectcan be captured. The contrast medium is consumed in a minimum amountthat is required, and hence the subject is prevented from being dosedwith an unduly excessive amount of contrast medium.

The various means referred to in the present invention may be arrangedto perform their stated functions, and may be implemented by dedicatedpieces of hardware for performing the functions, data processingapparatus for performing the functions according to computer programs,functions achieved in data processing apparatus according to computerprograms, or combinations thereof.

The various means referred to in the present invention are not requiredto be individually independent entities, and may be arranged such that aplurality of means may be constructed as a single apparatus, a certainmeans may be part of another means, or part of a certain means and partof another means overlap each other.

A computer unit referred to in the present invention may comprise apiece of hardware capable of reading the data of a computer program andperforming a processing operation according to the computer program, andmay comprise a CPU (Central Processing Unit) to which are connectedvarious devices including a ROM (Read Only Memory), a RAM (Random AccessMemory), an I/F (Interface) unit, etc.

According to the present invention, enabling a computer unit to carryout various operations according to a computer program also signifiesenabling the computer unit to control operation of various devices tocarry out various operations. For example, storing various data in acomputer unit may signify enabling a CPU to store various data in aninformation storage medium such as a RAM or the like fixedly mounted inthe computer unit, or enabling a CPU to store various data in aninformation storage medium such as an FD (Flexible Disc-cartridge) orthe like replaceably loaded in the computer unit through an FDD (FDDrive).

An information storage medium referred to in the present invention maycomprise a piece of hardware which stores in advance a computer programfor enabling a computer unit to perform various processing operations.An information storage medium may comprise, for example, a ROM or an HDD(Hard Disc Drive) fixedly mounted in the computer unit, or a CD (CompactDisc)-ROM or an FD replaceably loaded in the computer unit.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a logic structure of a liquid injectoraccording to an embodiment of the present invention;

FIG. 2 is a perspective view of the liquid injector;

FIG. 3 is a perspective view of a CT scanner as an imaging diagnosticapparatus;

FIGS. 4 a and 4 b are perspective view showing the manner in which aliquid syringe is set on an injection head of the liquid injector;

FIG. 5 is a block diagram of an electric circuit arrangement of theliquid injector;

FIG. 6 is a diagram showing a variable pattern of an injection rate;

FIG. 7 is a diagram showing a CT value representing an image contract asit varies with time;

FIG. 8 a flowchart of a processing sequence of the liquid injector;

FIG. 9 is a diagram showing a variable pattern of an injection rateaccording to a modification;

FIG. 10 is a diagram showing a CT value as it varies with time accordingto the modification; and

FIG. 11 is a diagram showing a CT value as it varies with time accordingto a conventional liquid injector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Arrangement of theLiquid Injector:

As shown in FIG. 2, liquid injector 100 according to an embodiment ofthe present invention comprises injection head 101 and main body 102.Main body 102 is mounted on the upper end of stand 103. Arm 104 isvertically mounted on a side wall of main body 102, and injection head110 is mounted on the upper end of arm 104.

As shown in FIG. 3, liquid injector 100 is used near imaging unit 301 ofCT scanner 300 which serves as an imaging diagnostic apparatus. Liquidinjector 100 injects a contrast medium as a liquid from liquid syringe200 into a subject (not shown) who is to be imaged by CT scanner 300.

As shown in FIG. 4, liquid syringe 200 comprises cylinder 201 and piston202 slidably inserted in cylinder 201. Injection head 101 of liquidinjector 100 holds cylinder 201 of syringe 200, which is replaceable, inrecess 106 that is defined in an upper surface of injection head 101.Injection head 101 has syringe actuating mechanism 107 as liquidinjection mechanism disposed behind recess 106. Syringe actuatingmechanism 107 grips piston 202 of syringe 200 that is held in recess 106and slides piston 202 into and out of cylinder 201.

As shown in FIG. 2, main body 102 has console panel 108 and liquidcrystal display panel 109. As shown in FIG. 5, console panel 108, liquidcrystal display panel 109, and syringe actuating mechanism 107 areconnected to computer unit 110. Computer unit 110 comprises CUP 111, ROM112, and RAM 113. A computer program and resources for CPU 111 arestored as software in at least one of ROM 112 and RAM 113.

When the CPU 111 reads the software from one of ROM 112 and RAM 113 andperforms various processing sequences based on the software, liquidinjector 100 logically has, as various means, various functionsincluding, as shown in FIG. 1, concentration storing function 121,coefficient storing function 122, data entering function 123,concentration reading function 124, coefficient reading function 125,total calculating function 126, total entering function 127, patternstoring function 128, and rate controlling function 129.

Concentration storing function 121 corresponds to a storage area that isconstructed in ROM 112 for CPU 111 to recognize data stored thereinaccording to the computer program. Concentration storing function 121stores the data of concentrations of an effective component contained inrespective different types of contrast mediums. More specifically, sincethere are available a plurality of different types of contrast mediumsfor CT which contain different concentrations of iodine as an effectivecomponent, ROM 112 stores the data of concentrations of iodine containedin the respective different types of contrast mediums.

Coefficient storing function 122 also corresponds to a storage area inROM 112 and stores the data of coefficients given to regions to beimaged of a subject. More specifically, since CT scanner 300 capturesimages of different regions, e.g., “head”, “chest”, etc. of a subject,ROM 112 stores the data of coefficients given to those regions to beimaged of the subject. These coefficients are used to calculate a totalamount of contrast medium to be injected into the subject, as describedlater on, and are set to appropriate values that are established for therespective regions to be imaged based on experimental results.

Data entering function 123 is a function for CPU 111 to recognize thedata of inputs that are entered into console panel 108, and enters thedata of the body weight of a subject, regions to be imaged of thesubject, and the type of a contrast medium used. The above functionscorrespond to functions for CPU 111 to perform predetermined processesaccording to the computer program. Concentration reading function 124reads the data of the concentration of iodine based on the entered typeof a contrast medium. Coefficient reading function 125 reads the data ofcoefficients corresponding to the regions to be imaged of a subject thathave been entered.

Total calculating function 126 calculates a total amount of contrastmedium to be injected into a subject in proportion to the body weight ofthe subject, in inverse proportion to the concentration of iodinecontained in the contract medium used, and depending on the coefficientsgiven to the regions to be imaged of the subject. Total enteringfunction 127 enters the data of the total amount of contrast medium tobe injected from total calculating function 126, and provides theentered data to rate controlling function 129.

More specifically, liquid injector 100 has registered therein totalamounts of contrast medium to be injected into subjects based on thebody weights of subjects, for example, as “A (g/Kg)” based onexperimental results. When the data of the body weight of a subject isentered as “B (Kg)”, a total amount of iodine in proportion to the bodyweight is calculated as “A×B (g)”.

Inasmuch as the data of concentrations of iodine contained in differenttypes of contrast medium are registered as “C (g/ml)”, when a type ofcontrast medium is entered, a total amount of the contrast medium to beinjected is calculated as “(A×B)/C (ml)” in inverse proportion to theconcentration. Furthermore, because the data of coefficients given todifferent imaging regions are registered as “D”, when the data of acertain region to be imaged is entered, a total amount of contrastmedium to be injected for the region to be imaged is calculated as“(A×B×D)/C (ml)”.

Pattern storing function 128 corresponds to a storage area of ROM 112,and stores therein the data of a variable pattern according to which theinjection rate of a contrast medium is to be varied with time. The dataof a variable pattern is set to maintain a state in which a CT valueserving as an image contrast approximates an optimum level.

Rate controlling function 129 controls operation of syringe actuatingmechanism 107 to inject a total amount of contrast medium that has beencalculated by total calculating function 126 into a subject over apredetermined period of time. Rate controlling function 129 also varies,with time the injection rate of the contrast medium according to thevariable pattern stored by pattern storing function 128. The variablepattern is set optimally based on experimental results, and is typicallyset such that, as shown in FIG. 6, the injection rate is linearlyreduced for a certain period of time from the start of injection, andsubsequently kept constant.

The above various functions of liquid injector 100 are accomplished bypieces of hardware such as console panel 108, they are mainlyimplemented by CPU 111 as a piece of hardware as it functions accordingto the resources and the computer program that are stored in aninformation storage medium such as ROM 112, etc.

The resources include registered data of total amounts of iodine to beinjected based on the body weights of subjects, a data file ofconcentrations of iodine contained in different types of contrastmediums, a data file of coefficients assigned to regions to be imaged ofsubjects, registered data of a variable pattern, etc. The computerprogram is stored in an information storage medium such as RAM 113, etc.as software for enabling CPU 111 to perform various processing sequencesto accept the entered data of the body weight of a subject, a regionthereof to be imaged, and the type of a contrast medium from consolepanel 108, read the data of a concentration of iodine from ROM 112 basedon the entered type of the contrast medium, read the data of acoefficient corresponding to the region to be imaged of the subject thathas been entered, calculate a total amount of contrast medium to beinjected into the subject in proportion to the body weight of thesubject, in inverse proportion to the concentration of iodine containedin the contract medium used, and depending on the coefficient given tothe region to be imaged of the subject, and control operation of syringeactuating mechanism 107 to inject the calculated total amount ofcontrast medium at an injection rate that varies with time according tothe variable pattern for a predetermined period of time.

Operation of the Liquid Injector:

For using liquid injector 100 according to the present embodiment, theoperator (not shown) connects liquid syringe 200 to the subject (notshown) placed in imaging unit 301 of CT scanner 300 with an extensiontube. Cylinder 201 of liquid syringe 200 is held in recess 106 ofinjection head 101, and piston 202 is gripped by syringe actuatingmechanism 107.

Then, the operator makes an input action on console panel 104 toinstruct liquid injector 100 to start operating. As shown in FIG. 8,liquid crystal display panel 109 displays a guidance message “ENTERNUMERICAL VALUE OF SUBJECT'S BODY WEIGHT IN KILOGRAMS. IF DEFAULT VALUEIS USED, ENTER 00, AND IF PREVIOUS NUMERICAL VALUE IS USED, ENTER 01.”in step S1.

The operator then enters the numerical value of the body weight of thesubject on console panel 108 in step S2. The entered numerical value ofthe body weight of the subject is stored in a working area of RAM 113.If “00” is entered, then a default value registered as an average bodyweight value is copied from ROM 112 to RAM 113. If “01” is entered, thenthe previous numerical value stored in RAM 113 is made effective.

Thereafter, liquid crystal display panel 109 displays a guidance message“ENTER REGION TO BE IMAGED WITH FOLLOWING NUMBER. HEAD=1, CHEST=2,ABDOMEN=1, LEG=4, ARM=2” in step S4. The operator enters a numberrepresenting a region to be imaged on console panel 108 in step S5.Based on the entered number, CPU 111 reads the data of a coefficientfrom a data file in ROM 112, and holds the data of the coefficient inRAM 113 in step S7.

Thereafter, liquid crystal display panel 109 displays a guidance message“ENTER TYPE OF CONTRAST MEDIUM TO BE USED WITH FOLLOWING NUMBER. xx CO.xx CONTRAST MEDIUM=1, . . . ” in step S8. The operator then enters anumber representing a type of contrast medium on console panel 108 instep S9. Based on the entered number, CPU 111 reads the data of aconcentration of iodine contained in the contrast medium ROM 112, andholds the data of the concentration in RAM 113 in step S11.

CPU 111 performs a calculating process to calculate a total amount ofcontrast medium to be injected by multiplying the total amount of iodinecontained in the contrast medium whose data is registered depending onthe body weight of the subject, by body weight of the subject, dividingthe multiplied amount by the concentration of contained iodine, andmultiplying the divided amount by the coefficient assigned to the regionto be imaged, in step S12.

Then, CPU 111 reads the data of the variable pattern from ROM 112 instep S13. CPU 111 generates the data of an injection patterncorresponding to the variable pattern for injecting the calculated totalamount of contrast medium in a predetermined period of time in step S14.For example, if the variable pattern is set according to a predeterminedwaveform as shown in FIG. 6, then the waveform of the variable patternis vertically moved with the injection time unchanged, so that the areasurrounded by the waveform and the x- and y-axes will be commensuratewith the total amount of contrast medium to be injected.

The operator then makes an input action on the console panel 108 tostart injecting the contrast medium in step S15. The CPU 111 controlsoperation of syringe actuating mechanism 107 according to the injectionpattern, thereby injecting the calculated total amount of contrastmedium at the injection rate that varies with time according to thevariable pattern, in the predetermined period of time in step S17.

Advantages of the Liquid Injector:

Since liquid injector 100 varies the injection rate of the contrastmedium with time according to the variable pattern, a state in which theCT value approximates the optimum level can be maintained, allowing CTscanner 300 to capture an optimum fluoroscopic image of the subject. Asthe contrast medium is consumed in a minimum amount that is required,the contrast medium can be saved without excessive consumption,contributing to the health of the subject.

An experiment was conducted in which a contrast medium was injected intoa subject according to a variable pattern such that the injection rateis linearly reduced for a certain period of time from the start ofinjection, and subsequently kept constant, as shown in FIG. 6. Theresults of the experiment has confirmed that a state in which the CTvalue approximates the optimum level as shown in FIG. 7 is maintainedfor a long period of time.

Furthermore, liquid injector 100 according to the present embodiment canautomatically calculate a total amount of contrast medium to be injectedinto a subject for a predetermined period of time when the body weightof the subject, a region to be imaged of the subject, and a type ofcontrast medium to be used are entered into liquid injector 100.Consequently, the operator is not required to carry out complexcalculations to determine a total amount of contrast medium to beinjected into the subject. In particular, inasmuch as liquid injector100 automatically generates an injection pattern depending on thecalculated total amount of contrast medium to be injected and thevariable pattern, the operator does not need to perform a complexprocess of varying the injection rate of the contrast medium with time.

Modifications:

The present invention is not limited to the above embodiment, butvarious changes and modifications may be made therein without departingfrom the scope of the invention. For example, as shown in FIG. 6, thevariable pattern such that the injection rate is linearly reduced for acertain period of time from the start of injection, and subsequentlykept constant is illustrated in the above embodiment. The variablepattern may be set to various data based on experimental results. Forexample, the injection rate may be varied nonlinearly.

The inventor of the present invention conducted an injection experimentwith a variable pattern such that the injection rate is linearly reducedfor a certain period of time from the start of injection, andsubsequently linearly increased. It has been confirmed from the resultsof the injection experiment that a state in which the CT valueapproximates the optimum level as shown in FIG. 10 is maintained for along period of time.

In the above embodiment, only the data of the body weight of a subjectis entered as a parameter of the subject in order to calculate a totalamount of contrast medium to be injected into the subject. However,various data of the height, gender, age, body shape, etc. of a subjectmay be used to calculate a total amount of contrast medium to beinjected into the subject. While it has been illustrated in the aboveembodiment that the operator enters a numerical value of the body weightof a subject, it is possible for the operator to select one of bodyweight ranges, e.g., “less than 10 (Kg), 10-20 (Kg), . . . ”.

In the above embodiment, the operator manually enters the data of thebody weight of a subject on console panel 108. However, as disclosed inJapanese patent application No. 2002-393968 filed by the applicant ofthe present application, if a medical record of a subject is availablein the form of electronic data, then the data of the body weight of thesubject may be read from the medical record.

Since CT scanner 300 has a bed for supporting the subject thereon, thebody weight of the subject may be measured using the bed and the datathereof may be entered into liquid injector 100. When the subject is tobe imaged by CT scanner 300, the data of a region to be imaged of thesubject is entered of necessity into CT scanner 300. Consequently, theentry of the data of a region to be imaged of the subject into CTscanner 300 and the entry of the data of a region to be imaged of liquidinjector 100 may be performed in common.

In the above embodiment, the operator enters the data of the type of acontrast medium to be used on console panel 108. However, as disclosedin Japanese patent application No. 2002-021762 filed by the applicant ofthe present application, the type of syringe 200 mounted on injectionhead 101 may be detected to determine the type of a contrast medium tobe used.

In the above embodiment, CT scanner 300 is used as an imaging diagnosticapparatus, and liquid injector 100 injects a contrast medium for usetherewith into subjects. However, an MIR apparatus may be used as animaging diagnostic apparatus, and liquid injector 100 may inject acontrast medium for use therewith into subjects.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

What is claimed is:
 1. A liquid injector for injecting a contrast mediuminto a subject whose fluoroscopic image is to be captured by an imagingdiagnostic apparatus, comprising: a liquid injection mechanism forinjecting said contrast medium into said subject; pattern storing meansfor registering data of a variable pattern in which an injection rate ofthe contrast medium for keeping an image contrast of the fluoroscopicimage within a predetermined range varies with time; and ratecontrolling means for varying an operating speed of said liquidinjection mechanism with time according to said variable pattern.
 2. Theliquid injector according to claim 1, wherein said pattern storing meanscomprises means for registering the data of the variable pattern inorder to maintain a state in which the image contrast of thefluoroscopic image that is produced by said contrast medium approximatesan optimum level.
 3. The liquid injector according to claim 1, furthercomprising: total amount entering means for accepting entered data of atotal amount of the contrast medium to be injected into the subject;said rate controlling means comprising means for increasing or reducingsaid injection rate in elapsed times according to said variable patterndepending on said total amount of the contrast medium to be injectedinto the subject.
 4. The liquid injector according to claim 3, furthercomprising: data entering means for accepting entered data of the bodyweight of the subject; and total calculating means for increasing orreducing said total amount of the contrast medium to be injected intothe subject in proportion to the body weight whose data has been enteredby said data entering means.
 5. The liquid injector according to claim3, further comprising: coefficient storing means for registering data ofpredetermined coefficients assigned to respective regions to be imagedof the subject; data entering means for accepting entered data of aregion to be imaged of the subject; coefficient reading means forreading the data of one of the coefficients from said coefficientstoring means depending on the region to be imaged of the subject whosedata has been entered by said data entering means; and total calculatingmeans for correcting said total amount of the contrast medium to beinjected into the subject by multiplying said total amount by thecoefficient whose data has been read by said coefficient reading means.6. The liquid injector according to claim 3, wherein said contractmedium is available in a plurality of types having differentconcentrations of an effective component contained therein, furthercomprising: concentration storing means for registering data of thedifferent concentrations in the types of said contract medium; dataentering means for accepting entered data of a type of the contrastmedium; concentration reading means for reading data of theconcentration from said concentration storing means depending on thetype of the contrast medium whose data has been entered by said dataentering means; and total calculating means for increasing or reducingsaid total amount of the contrast medium to be injected into the subjectin inverse proportion to said concentration whose data has been read bysaid concentration reading means.
 7. The liquid injector according toclaim 3, wherein said contract medium is available in a plurality oftypes having different concentrations of an effective componentcontained therein, further comprising: concentration storing means forregistering data of the different concentrations in the types of saidcontract medium; coefficient storing means for registering data ofpredetermined coefficients assigned to respective regions to be imagedof the subject; data entering means for accepting entered data of atleast the body weight of the subject, a region to be imaged of thesubject, and one of the types of the contrast medium; concentrationreading means for reading data of the concentration from saidconcentration storing means depending on the type of the contrast mediumwhose data has been entered by said data entering means; coefficientreading means for reading the data of one of the coefficients from saidcoefficient storing means depending on the region to be imaged of thesubject whose data has been entered by said data entering means; andtotal calculating means for correcting said total amount of the contrastmedium to be injected into the subject, which has been increased orreduced in proportion to said body weight and in inverse proportion tosaid concentration, by multiplying said total amount by said one of thecoefficients.
 8. A method of injecting a liquid with a liquid injectoraccording to claim 1, comprising the step of: varying an injection rateof said contrast medium with time according to said variable pattern. 9.The method according to claim 8, further comprising the steps of:accepting entered data of a total amount of the contrast medium to beinjected into the subject; and increasing or reducing said injectionrate in elapsed times according to said variable pattern depending onsaid total amount of the contrast medium to be injected into thesubject.
 10. The method according to claim 9, wherein said contractmedium is available in a plurality of types having differentconcentrations of an effective component contained therein, furthercomprising the steps of: registering data of the differentconcentrations in the types of said contract medium; registering data ofpredetermined coefficients assigned to respective regions to be imagedof the subject; accepting entered data of at least the body weight ofthe subject, a region to be imaged of the subject, and one of the typesof the contrast medium; reading data of the concentration depending onthe type of the contrast medium whose data has been entered; reading thedata of one of the coefficients depending on the region to be imaged ofthe subject whose data has been entered; and correcting said totalamount of the contrast medium to be injected into the subject, which hasbeen increased or reduced in proportion to said body weight and ininverse proportion to said concentration, by multiplying said totalamount by said one of the coefficients.
 11. A computer unit forcontrolling operation of a liquid injection mechanism of a liquidinjector for injecting a contrast medium into a subject whosefluoroscopic image is to be captured by an imaging diagnostic apparatus,comprising: pattern storing means for registering data of a variablepattern in which an injection rate of the contrast medium varies withtime; and rate controlling means for varying an operating speed of saidliquid injection mechanism with time according to said variable pattern.12. The computer unit according to claim 11, further comprising: totalamount entering means for accepting entered data of a total amount ofthe contrast medium to be injected into the subject; said ratecontrolling means comprising means for increasing or reducing saidinjection rate in elapsed times according to said variable patterndepending on said total amount of the contrast medium to be injectedinto the subject.
 13. The computer unit according to claim 12, whereinsaid contract medium is available in a plurality of types havingdifferent concentrations of an effective component contained therein,further comprising: concentration storing means for registering data ofthe different concentrations in the types of said contract medium;coefficient storing means for registering data of predeterminedcoefficients assigned to respective regions to be imaged of the subject;data entering means for accepting entered data of at least the bodyweight of the subject, a region to be imaged of the subject, and one ofthe types of the contrast medium; concentration reading means forreading data of the concentration from said concentration storing meansdepending on the type of the contrast medium whose data has been enteredby said data entering means; coefficient reading means for reading thedata of one of the coefficients from said coefficient storing meansdepending on the region to be imaged of the subject whose data has beenentered by said data entering means; and total calculating means forcorrecting said total amount of the contrast medium to be injected intothe subject, which has been increased or reduced in proportion to saidbody weight and in inverse proportion to said concentration, bymultiplying said total amount by said one of the coefficients.
 14. Acomputer program for enabling a computer unit according to claim 11 tocarry out a process of varying an operating speed of said liquidinjection mechanism with time according to said variable pattern. 15.The computer program according to claim 14 for enabling said computer tocarry out a process comprising the steps of: accepting entered data of atotal amount of the contrast medium to be injected into the subject; andIncreasing or reducing said injection rate in elapsed times according tosaid variable pattern depending on said total amount of the contrastmedium to be injected into the subject.
 16. A computer program accordingto claim 15, wherein said contract medium is available in a plurality oftypes having different concentrations of an effective componentcontained therein, said computer program enabling said computer to carryout a process comprising the steps of: registering data of the differentconcentrations in the types of said contract medium; registering data ofpredetermined coefficients assigned to respective regions to be imagedof the subject; accepting entered data of at least the body weight ofthe subject, a region to be imaged of the subject, and one of the typesof the contrast medium; reading data of the concentration depending onthe type of the contrast medium whose data has been entered; reading thedata of one of the coefficients depending on the region to be imaged ofthe subject whose data has been entered; and correcting said totalamount of the contrast medium to be injected into the subject, which hasbeen increased or reduced in proportion to said body weight and ininverse proportion to said concentration, by multiplying said totalamount by said one of the coefficients.
 17. An information storagemedium storing therein a computer program according to claim 14, whichis to be read by a computer unit.